DESIGN AND SYNTHESIS OF DONOR ACCEPTOR HYBRIDIZED SMALL MOLECULES AND GRAPHENE DERIVATIVES FOR PHOTOVOLTAIC AND OPTICAL STUDIES ANUPAM MIDYA NATIONAL UNIVERSITY OF SINGAPORE 2011 DESIGN AND SYNTHESIS OF DONOR ACCEPTOR HYBRIDIZED SMALL MOLECULES AND GRAPHENE DERIVATIVES FOR PHOTOVOLTAIC AND OPTICAL STUDIES ANUPAM MIDYA M.Sc. (Chemistry), IIT-Kharagpur A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2011 Acknowledgements Doing research in science abroad is not a smooth job for a person who has studied in his school days under a kerosene lamp in a remote village. Therefore, first of all, I would like to express my heartfelt gratitude to my supervisor Associate Professor Loh Kian Ping for selecting me as a Ph.D. student in his group and for his advice and guidance throughout my Ph.D. life. I am very fortunate to work under a great academic supervisor like him. I appreciate the number of hours he has devoted in giving suggestions and ideas so as to make my Ph.D. experience productive and stimulating. With his enormous financial support I was able to successfully carry out my experiments. The joy and enthusiasm he has for his research was contagious and was a motivational factor for me even during tough periods in my Ph.D. Next, I want to thank my co-supervisor, Dr. Chen Zhi-Kuan for giving me a well equipped lab in Institute of Materials Research and Engineering (IMRE). His expertise in organic synthesis has certainly helped me very much in my Ph.D. pursuit. My time in IMRE was smooth and enjoyable because of all the friendly and helpful colleagues in Dr. Chen’s group. I take this opportunity to specially thank Dr. Yao Junhong who unselfishly guided me through the learning of organic synthesis during the initial days of my research. I would like to acknowledge everyone in Professor Loh’s group who has supported me in numerous ways, particularly Dr. Yang Jia-Xiang, Dr. Zhong Yulin, Mr. Kiran Kumar Manga, Dr. Chong Kwok Feng, Dr. Wang Junzhong, Ms. Candy Lim, Mr. Lu Jiong, Dr. Zhang Xuanjun, Dr. Bao Qiaoliang, Dr. Deng Suzi, Dr. Hoh Hui Ying, Ms. Priscilla Kai Lian Ang, Mr. Janardhan bolapanaru, Ms. Lena, Ms. Goh Bee Min, Dr. Wang Shuai. All of them stood by me, rendering their sincere help, when I did my experiments and also sharing valuable ideas and thoughts, as and when I needed them. I would like to thank Prof. Stefan Adams and Dr. Xie Zhibin who helped me by fabricating dye sensitized solar cell devices at material science department in NUS. It gives me immense pleasure to thank Prof. Ji Wei and Mr. Venkatesh Mamidala who helped me by performing nonlinear optical measurement at physics department in NUS. I wish to thanks all my friends in NUS, specially Dr. Manoj Kumar Manna and Mr. Kaushik Ghosh for their help in revising my thesis. I am really grateful to my whole family, especially my parents for their continuous support, motivation and unconditional care throughout my career and in every aspect of my life. Without their encouragement and understanding it would have been impossible for me to bring my Ph.D. to a successful completion. I Publications 1. Yulin Zhong, Kian Ping Loh, Anupam Midya, and Zhi-Kuan Chen “Suzuki Coupling of Aryl Organics on Diamond”, Chemistry of Materials 2008, 20, 3137. 2. Yulin Zhong, Anupam Midya, Zhaouye Ng, Zhi-Kuan Chen, M Daenen, M Nesladek,and Kian Ping Loh, “Diamond-based Molecular Platform for Photoelectrochemistry”, Journal of the American Chemical. Society 2008, 130, 17218. 3. Zhibin Xie,+ Anupam Midya,+ Kian Ping Loh, Stefan Adams, Daniel J Blackwood, John Wang, Xuanjun Zhang, and Zhi-kuan Chen, “Highly efficient dye-sensitized solar cells using phenothiazine derivative organic dyes” Progress in Photovoltaic: Research and Application 2010, 18, 573 (+both authors contributed equally to this work). 4. Anupam Midya, Zhibin Xie, Jia-Xiang Yang, Zhi-Kuan Chen, Daniel J Blackwood, John Wang, Stefan Adams, Kian Ping Loh, “A new class of solid state ionic conductor for application in all solid state dye sensitized solar cells” Chemical Communications 2010, 46. 2091. 5. Anupam Midya, Venkatesh Mamidala, Jia-Xiang Yang, Priscilla Kai Lian Ang, Zhi-Kuan Chen, Wei Ji, Kian Ping Loh, “Synthesis and Superior Optical-Limiting Properties of Fluorene-Thiophene-Benzothiadazole Polymer-Functionalized Graphene Sheets” Small 2010, 6, 2292. 6. Zhi Bin Xie, Anupam Midya, Kian Ping Loh, Daniel J. Blackwood “Enhanced efficiency of phenothiazine derivative organic dye sensitized ionic liquid solar cells on ageing’ Progress in Photovoltaic: Research and Application, submitted. II Table of Contents Acknowledgements I Publications .II Table of Contents .III Abstract VII List of Tables .IX List of Figures .X List of Schemes XV Chapter 1: Introduction 1.1. 1-29 Introduction to organic solar cell .1 1.1.1. Motivation and background .2 1.1.2. Organic semiconductor 1.1.2.1. Photoinduced charge generation and transport 1.1.2.2. Chemical structure and bandgap energy 1.1.2.3. Molecular structure and solubility .11 1.1.3. Organic solar cell .12 1.2. 1.1.3.1. Device performance .14 1.1.3.2. Bulk heterojunction 16 1.1.3.2. Dye sensitized solar cell .18 1.1.3.2. Solid state dye sensitized solar cell 21 Introduction to graphene based materials for optical application 22 III 1.3. References 23 Chapter 2: Small molecule for bulk heterojunction solar cell 30-67 2.1. Introduction 30 2.2. Experimental 34 2.2.1. Materials and characterization .34 2.2.2. Synthesis of small molecular dyes .35 2.2.3. Solar cell device structure 54 2.3. Result and discussion .55 2.3.1. Photo physical property .55 2.3.2. Electrochemical properties .60 2.3.3. Thermal properties .62 2.3.4. Solar cell device performance 63 2.4. Conclusion .65 2.5. References .65 Chapter 3: Phenothiazine based efficient organic dye for dye sensitized solar cell 68-103 3.1. Introduction 68 3.2. Experimental 74 3.2.1. Materials and characterization .74 3.2.2. Synthesis of phenothiazine based dyes 76 3.2.3. Fabrication of the DSSCs .86 3.3. Result and discussion .88 3.3.1. Electrochemical properties .88 3.3.2. Optical properties .90 IV 3.3.3. Photovoltaic performances of the DSSCs 92 3.3.4. Electrochemical Impedance measurement .96 3.4. Conclusion .100 3.5. References 101 Chapter 4: Solid state conductor for solid state dye sensitized solar cell 104-123 4.1. Introduction 104 4.2. Experimental 107 4.2.1. Material and characterization .107 4.2.2. Synthesis of solid state conductor 107 4.2.3. Device structure and characterization 112 4.3. Result and discussion .113 4.3.1. Electrochemical properties .113 4.3.2. Photovoltaic performance 114 4.3.3. KI effect .117 4.3.3. Measurement of triiodide diffusion coefficient .119 4.4. Conclusion .121 4.5. References 122 Chapter 5: Graphene-polymer hybrid for nonlinear optics 124-154 5.1. Introduction 124 5.2. Experimental 127 5.2.1. Materials and characterization .127 5.2.2. Synthesis of graphene-organic hybrid .128 5.3. Result and discussion .133 5.3.1. Synthesis and characterization .133 V 5.3.2. Electrochemical properties .137 5.3.3. Photophysical properties 139 5.3.4. FTIR study .141 5.3.5. Thermal properties .142 5.3.6. Morphology and grafting behavior of G-Polymer .143 5.3.7. Optical limiting properties .148 5.3.8. Nonlinear scattering behavior 149 5.4. Conclusions 151 5.5. References 152 Chapter 6: Conclusions and outlook 155-159 6.1. Conclusions 155 6.2. Outlook 158 Appendices: .160-181 VI Abstract The limited energy source and environmental problems created by greenhouse gases and other pollutants from detrimental fossil fuel by product provides the driving force for researching on renewable energy source- solar energy. In the first part of this thesis, the fundamentals of organic photovoltaics are discussed followed by introducing three types of organic semiconducting materials and their applications in organic solar cells. In the second chapter of this thesis, a series of small molecules have been synthesized and attempted them in molecular bulkheterojunction (BHJ) solar cell. The band gap energy of the small molecules can be tuned according to the strength of the donor moiety. The special configuration of phenothiazine donor moiety improves the film-making properties. In chapter 3, a novel donor-spacer-acceptor (D-π-A) type organic dye has been synthesized using phenothiazine donor, vinyl-bithiophene spacer and cyanoacrylic acid acceptor and highly efficient dye-sensitized solar cell (DSSC) have been fabricated using liquid electrolyte. Structural modification by introducing two donor moieties to the D-π-A system improves the photoabsorption capacity but does not lead to improvement of efficiency. To address the problem associated with liquid electrolyte in DSSCs, a new class of solid state ionic conductor as electrolyte for solid-state dye sensitized solar cell (SDSC) has been developed in chapter 4. The well-known hole conductor carbazole is attached to imidazolium iodide structure and successfully deployed as solid state ionic conductor in SDSCs. The combined solid state ionic conductors and iodine electrolytes provides dual channels for hole/triiodide transportation in SDSC. In the last part of this thesis, a generic functionalization method based on VII Suzuki coupling and diazonium coupling has been developed to synthesize graphenepolymer hybrids. Reduced graphene oxide sheets are grafted with semiconducting D-π-A type polymer. Although these hybrids not show useful photovoltaic response, they exhibit more superior optical limiting properties compared to benchmark optical limiting materials. VIII NC NC S S N C6H13 CBZ-dye S S NC CN H NMR (CDCl3 , 400 MHz) 166 N C8H17 S S S PTZ-1 NC CO2H H NMR (CD CO CD , 400 MHz) 167 N C8H17 N SCNN+ C6H13 SD1 H NMR (CD Cl2 , 400 MHz) 168 N C8H17 N I- N+ CH3 SD2 H NMR (CD Cl2 , 400 MHz) 169 N C8H17 N IN+ C6H13 SD3 H NMR (CD Cl2 , 400 MHz) 170 MS (MALDI-Tof) CN S S S NC N C8H17 PTZ-dye Calcd m/z = 577.168 171 MS (MALDI-Tof) C12H25 N CN NC NC S S S S S CN PTZ-dye Calcd m/z = 847.196 172 MS (MALDI-Tof) C8H17 N CN S S S CN S S N C8H17 PTZ-dye Calcd m/z = 994.326 173 MS (MALDI-Tof) CN NC S NC S S C8H17 S CN C8H17 FLR-dye Calcd m/z = 870.291 174 MS (MALDI-Tof) OC12H25 NC NC NC S S S S CN C12H25O OPE-dye Calcd m/z = 974.265 175 MS (MALDI-Tof) NC CN NC S NC S S S N C6H13 CBZ-dye Calcd m/z = 731.130 176 MS (MALDI-Tof) S S N C8H17 S CO2H NC PTZ-1, Calcd m/z = 596.825 177 MS (MALDI-Tof) C8H17 N S S N C8H17 S S CO2H S NC PTZ-2 Calcd m/z = 1014.324 178 MS (MALDI-Tof) SCNN+ C6H13 N N C8H17 SD1 Calcd m/z (M-SCN) = 430.322 MS (MALDI-Tof) 179 IN+ CH3 N N C8H17 SD-2 Calcd m/z for (M-I) = 360.244 180 MS (MALDI-Tof) IN+ C6H13 N N C8H17 SD-3 Calcd m/z for (M-I) = 430.322 181 [...]... top level of the filled (i.e HOMO) band and the bottom level of the empty (i.e LUMO) band is the band gap energy which is largely responsible for the electronic and optical properties of the conjugated systems Figure 1.1 Hybridization of the atomic orbitals (b) and formation of bonds (a) for two sp2 -hybridized carbon atoms 3 Figure 1.2 A schematic diagram of energy levels, hybridization of atomic orbitals... parameters of the SDSCs using different electrolytes under the STC .116 IX List of Figures Figure 1.1 Hybridization of the atomic orbitals (b) and formation of bonds (a) for two sp2 -hybridized carbon atoms 3 Figure 1.2 A schematic diagram of energy levels, hybridization of atomic orbitals creates two continuous band states of filled and empty i.e HOMO and LUMO Eg is the band gap... (calcium, magnesium, gold and others are also used) Upon photoexcitation, exciton is created in either phase (mainly at donor phase) of the active material in the first step After that the exciton diffused to the interface of the donor and acceptor material and split into hole and electron For efficient charge separation, the HOMO and LUMO energy levels of p-type (Donor) and n-type (Acceptor) materials should... main disadvantage of the BHJ cell is the low mobility of the charge carrier through p-type and n-type materials and the unconnected island of donor and acceptor phase which has no influence on the efficiency 1.1.3.3 Dye Sensitized Solar Cell: The problem of low mobility and unconnected island in BHJ is overcome by adsorbing a monolayer of photochromator onto inorganic semiconductor and using redox electrolyte... illumination and (b) IPCE of the corresponding DSSCs .93 Figure 3.6 (a) J–V characteristics of the PTZ-1 based DSSCs under AM 1.5 100 mW/cm2 illumination and dark The IPCE of the device is displayed in inset) (b) The Jsc and Voc dependence of the light intensity for the device The lines are linearly and logically fitting for Jsc and Voc, respectively 96 Figure 3.7 EIS of DSSCs based on PTZ1 and PTZ2-CDCA... energy gap can be attained when the HOMO levels of the donor and the LUMO levels of the acceptor moiety are remain as close in energy in conjugation chain as shown in Figure 1.4 Thus, reduction in band gap is possible by enhancing the strength of donor and acceptor moieties via strong orbital interactions 9 In addition, conjugated molecules show lower band gap in solid phase compared to the solution... polymer and small molecules were used as photon harvesting semiconductor in plastic solar cell to generate current and a maximum efficiency of 6.5% achieved 5 In 1991, Professor Gratzel developed a new concept of dye sensitized solar cell 6 which combines the advantage of the highly conducting inorganic part and the ease of processing for the organic semiconductor part To date, an efficiency of 11%... structure and band gap energy: Band gap energy of a system can be tuned by hybridization of many non degenerate molecular orbitals in a conjugated length, as decrease in band gap energy is shown in Figure 1.2 with increasing conjugation length During the progress of conjugation, the HOMO and LUMO levels of the repeating unit disperse into the valence and conduction bands which ultimately decrease the band... reduced band gap when they are attached to conjugated units Using combinations of these donor and acceptor groups, a variety of low band gap 10 chromophores or dye have been synthesized 22 Thus, molecular engineering (e.g changing the length and functional group of polymers) can change the energy gap, which allows chemical change in these materials to generate variety of organic materials for device... maxima, J sc and V oc , 15 respectively This is a key quantity used to measure cell performance It is a measure of the squareness of the J–V curve The formula for FF in terms of the above quantities is FF = J mpp × Vmpp J sc × Voc Incident photon to electron conversion efficiency (IPCE): IPCE is the ratio of the number of charge carriers collected by the solar cell to the number of photons of a given . DESIGN AND SYNTHESIS OF DONOR ACCEPTOR HYBRIDIZED SMALL MOLECULES AND GRAPHENE DERIVATIVES FOR PHOTOVOLTAIC AND OPTICAL STUDIES ANUPAM MIDYA NATIONAL UNIVERSITY OF. UNIVERSITY OF SINGAPORE 2011 DESIGN AND SYNTHESIS OF DONOR ACCEPTOR HYBRIDIZED SMALL MOLECULES AND GRAPHENE DERIVATIVES FOR PHOTOVOLTAIC AND OPTICAL STUDIES ANUPAM MIDYA. second chapter of this thesis, a series of small molecules have been synthesized and attempted them in molecular bulkheterojunction (BHJ) solar cell. The band gap energy of the small molecules can